1. Field of the Invention
The present invention relates to an image capture device and more particularly relates to an image capture device with an optical image stabilization (OIS) function.
2. Description of the Related Art
Japanese Patent Application Laid-Open Publication No. 2009-272890 discloses a digital camcorder with two different kinds of OIS functions, one of which is an optical one and the other an electronic one. That digital camcorder senses its own shake by using an angular velocity sensor, and then compensates for its own shake by using both of the optical and electronic OIS functions in combination.
As a result, that digital camcorder achieves a significantly larger angle of stabilization, and therefore, can stabilize the image sufficiently even if the shake has great amplitude.
However, the digital camcorder disclosed in Japanese Patent Application Laid-Open Publication No. 2009-272890 realizes the optical and electronic OIS functions by always using the angular velocity sensor to sense its own shake. That is why the precision of stabilization solely depends on the sensibility of the angular velocity sensor. More specifically, the digital camcorder disclosed in Japanese Patent Application Laid-Open Publication No. 2009-272890 cannot sense its own subtle shake accurately enough to go beyond the limit of sensibility of the angular velocity sensor. Consequently, such a digital camcorder cannot accurately compensate for the image shakiness caused by that subtle shake.
FIG. 9(a) illustrates the waveform of a shake actually given to a digital camcorder. In FIG. 9(a), the abscissa represents the time and the ordinate represents the angular velocity to cancel the shake. It can be seen that a shake waveform with relatively low frequencies and a shake waveform with relatively high frequencies are superposed one upon the other in this waveform. It is only natural because when a digital camcorder is given a shake, high frequency components will represent a shake caused by hand or body tremors with small amplitudes and low frequency components will represent a shake caused by such tremors with bigger amplitudes, generally speaking.
On the other hand, FIG. 9(b) illustrates the waveform of a shake that has been sensed by the angular velocity sensor in the digital camcorder. This is a waveform corresponding to the low-frequency shake waveform shown in FIG. 9(a) and not including the high-frequency shake waveform. This is because the sensibility of the angular velocity sensor is not high enough to detect the high-frequency shake waveform. It should be noted that even if the angular velocity sensor could obtain such a high-frequency shake waveform, the amplitude of that waveform would be approximately equal to that of noise components that affect a signal indicating the sensing result obtained by the angular velocity sensor. For that reason, actually it should be difficult for another signal processor, which receives the output signal of the angular velocity sensor, to distinguish such a high-frequency shake waveform from the noise components.
FIG. 9(c) shows what waveform will be generated if the waveform shown in FIG. 9(a) is corrected based on the sensing result obtained by the angular velocity sensor. It can be seen that the corrected waveform is not quite flat and that the high-frequency shake waveform still remains partially.
In conventional digital camcorders, the influence of such high-frequency shake on the image quality of the video shot has not been considered to be important. This is because the sensitivities and resolutions of conventional imagers have been too low to cause a sensible influence on the image quality for general users.
Recently, however, as the sensitivities and resolution of imagers have been more and more increased and as the performance of lenses has been further improved, the influence of such a high-frequency shake on the image quality of video shot has become more and more easily sensible.